For example, an aluminum sheet is in the manufacture processes of the aluminum thinning sheet and the aluminum foil when the aluminum sheet is rolled to be thinned, a surface thereof becomes a mirror-smooth state increasingly in response to increase of the moving speed. In the manufacture processes of such aluminum sheet and aluminum foil, the aluminum thinning sheet and the aluminum foil which is uniform in thickness and excellent in quality without a pin hole can be obtained by controlling a temperature and the moving speed of the moving aluminum sheet in the rolling process. In the case of measurement of temperature of an object being not moved, in general, the contact-type thermometer using a thermocouple as a temperature sensitive element is used, since it is compact in size and excellent in the measurement accuracy, in addition, durable and further, a low price.
Moreover, for example, when a dangerous object that the actual temperature can not be measured in close proximity due to a high temperature such as an inside of a blast furnace and the object positioned at the high elevations as an insulator of a high voltage transmission line and moreover, the dangerous place that there is the transmission line on which high voltage is supplied are measured, a radiation thermometer detecting the infrared energy radiated from the object thereof is used.
In the contact-type thermometer using the thermocouple, one of the type that a contact plate is arranged on the tip portion of a temperature measuring portion to fix a temperature sensitive portion (a contact point) of thermocouple wires on the back thereof is used greatly, and the thermometer is designed to measure in such manner that the temperature measuring portion in which there is said temperature sensitive portion is pressed against the object slightly. On the occasion of this measurement, the thermometer is designed to press the temperature measuring portion of the tip portion of the thermometer at the right angle against a surface of the object to be measured on temperature to hold under the condition of laying the contact plate along the surface thereof to accurately transmit the temperature of an object to be measured on temperature to the temperature sensitive portion of the thermocouple provided behind the contact plate.
As described above, in the case of measuring a accurate temperature using the contact-type thermometer, it is a condition that the object to be measured on temperature is standing still, but in contrast with this, in the case that the object to be measured on temperature is moving, the force to move in the movement direction thereof with frictional resistance by contacting with this moving object to be measured acts on the contact plate and the front side of the contact plate is pulled, so that the rear side is floated to be inclined to become unstable.
When this contact plate is pulled to be moved, the thermocouple attached thereto also is dragged to be moved in the same direction. Moreover, this contact plate becomes deformed in the form of a concave, so that the contact condition is ready to become unstable, therefore, it becomes the condition that the temperature sensitive portion of the thermocouple fixed behind the central portion of the contact plate is floated more than the surface of the object to be measured on temperature. when, thus, the contact plate is floated more than the surface of the object to be measured on temperature, a thin air layer between this temperature sensitive portion and the surface of the object to be measured is formed, and a temperature error caused by this air layer, whereby measuring the accurate temperature becomes difficult.
The contact-type thermometer using a thermocouple is not adapt to the thermometer for the moving surface, whereby it can not be used widely except the case of measuring an approximate temperature of the moving object.
On the other hand, the radiation thermometer measures the infrared energy radiated from the object to be measured on temperature, whereby the temperature of an object being standing still, as a matter of course, and the moving object also can be measured.
However, this radiation thermometer is remarkably expensive as compared to the thermocouple type thermometer, in addition, a big error in the measured value can be resulted depending upon the presence or absence of a color of the object and a luster such as the aluminum foil, and furthermore, the presence or absence of a property being optically transparent such as a glass.
Moreover, there is an essential problem that the measured value is influenced greatly depending upon an atmosphere of the path through which the infrared energy radiated from the object passes, for example, whether the measurement place are filled with vapors, smoke and gases or not and a degree of the concentration such as the vapors, whereby a correction is required considerably in order to measure a accurate temperature in addition, an experience is required in an operation also.
Therefore, when measuring a temperature using this thermometer, the measured value should be designed to correct the measured value in advance after obtaining a reflection factor or a transmission factor of the object to be measured on temperature in advance. Moreover, since the emissivity, the reflection factor or the condition (the generation of vapor and smoke) of the space through which infrared rays transmits are changed frequently during using, there is a problem that it is required to correct the measured value thereof with the passage of time.